Islamic State militants drive on a new road they built through the Syrian-Iraq border in Nineveh province on June 9. / Al-Baraka News via AFP/Getty Images

by Oren Dorell, USA TODAY

by Oren Dorell, USA TODAY

Authorities in France and Morocco detained citizens suspected of joining the Islamic State, but a U.S. intelligence bulletin issued Friday said there are no specific or credible threats on the U.S. homeland from the militant group.

The FBI and Homeland Security Department issued the bulletin as concerns rise that Islamic State supporters in the USA and Europe could attack anywhere with little or no warning.

White House Deputy National Security Advisor Ben Rhodes told reporters Friday "we monitor very closely whether or not ISIL will seek to develop plots that are aimed at the West, aimed at beyond this geographic area where they've been operating. We are doing that. We're actively consulting with European partners about how to watch the threat that they could pose to the West. We take their threats seriously, because we have to take every threat that's made against the United States seriously." But he said there is no indication the group is at this point planning a 9/11-type of attack on the U.S.

U.S. law enforcement has been trying to identify Islamic State supporters who would bring the group's brand of violent jihad to the United States. U.S. airstrikes against the group in Iraq intensified after militants beheaded American journalist James Foley. The group called Foley's killing revenge for previous strikes against militants in Iraq.

French authorities on Friday detained two girls, ages 15 and 17, using a security net to find citizens considering travel to other countries to join jihad.

France is prosecuting suspects who try to become foreign fighters, even before they leave French soil. Thousands of European citizens have traveled to Syrian battlegrounds, but there is no unified plan in Europe to prevent them from going or to deal with them when they return.

France, which has a Muslim population of about 5 million - the largest in Western Europe - is leading the way on the continent. French authorities say there are some 900 people from France who have fought in a religious war abroad, plan to join one, or are returning from one. Several dozen have been killed.

A proposed law would allow passports to be confiscated from suspects planning to fight in Syria or Iraq and would create new measures to prosecute jihad wannabes or returnees. France also is planning to join other European countries in blocking Internet sites that espouse the jihad cause.

French Interior Minister Bernard Cazeneuve pointed to the man suspected of killing four people at the Jewish Museum in Brussels in May as evidence of the need to consider tough new measures to be debated this fall. The suspect, Frenchman Mehdi Nemmouche, fought in Syria.

"Must I wait for a new Mehdi Nemmouche to fire before I act?" Cazeneuve said in a recent interview with online publication Mediapart. Not all the proposed anti-terrorism measures will compromise civil liberties, he said.

Morocco also announced Friday the arrest of two suspected members of the Islamic State. The men, who had connections to foreign extremists, were planning to train in Syria with the group before returning to carry out attacks in Morocco, according to the government statement.

The Moroccan military is on high alert, stationing anti-aircraft missile batteries around major cities, as well as along the borders with Algeria and Mauritania. There has been no official explanation for the sudden high visibility of military units around the country, but the local press has said it is in response to fears of a terrorist attack related to two Airbus airliners stolen recently in Libya.

Morocco says at least 1,000 of its citizens are fighting on the side of Islamic extremists in Syria and Iraq.

Similar concerns occupy authorities in Britain and Germany as well.

"It is impossible to quantify the risk of terrorist attacks by returning foreign fighters," Nigel Inkster, a former counterterrorism chief for Britain's M16 spy agency, wrote Friday on his blog for the International Institute of Strategic Studies. But he said those returning from Syria and Iraq "are likely to be better trained and motivated and more battle-hardened" than those who trained in Pakistan's tribal areas over the past decade.